docs: def is_causal_sink(graph: BELGraph, node: BaseEntity) -> bool:
      """Return true if the node is a causal sink.
  
      - Does have causal in edge(s)
      - Doesn't have any causal out edge(s)
      """
      return has_causal_in_edges(graph, node) and not has_causal_out_edges(graph, node)